This invention relates to a capacitor discharge ignition system that is especially useful for jet engines. The invention is more particularly related to power factor correction of the AC input circuit of a capacitor discharge ignition system.
Jet engines require an ignition system that continuously causes a spark (2 per second) at a spark plug during the operation of the jet engine. The continuous spark assures that the fuel will remain ignited. It is a requirement of an ignition system for a jet engine that an electrical discharge, of a predetermined amount of energy, occur at the plug at the specified rate so as to assure combustion of the fuel. Therefore, one reason why combustion does not occur is that there is insufficient electrical energy in the electrical discharge to cause combustion of the fuel in the jet engine. Because of space limitations, weight limitations and electrical wiring limitations, jet engine manufacturers generally limit the size of the ignition system as well as the current that may flow into a circuit at a particular power level which requires certain minimum energy levels. The space and weight limitations are obviously necessary because the more weight added to an aircraft the larger the engine must be. Similarly, the more current that flows through conductors the larger the cabling and, hence, the weight of the cables.
Certain jet engines require a capacitor discharge ignition system that must store nine joules of energy in a storage capacitor while the AC input current to a transformer in the circuit must be equal to or less than one AMP. To limit the AC current in the circuit, some transformers utilize the inductive decoupling between the primary and the secondary windings to provide an input for the purpose of limiting the current in the primary windings of the transformer. The foregoing type transformer also causes a lagging power factor, i.e., the current reaches its peak value after the voltage reaches its peak value. Therefore, in the foregoing type of system there is a reduced power factor. This is a disadvantage because the current required to power such a system must be increased to obtain the same amount of output power as a system without a lagging power factor. This problem led to the search of a power factor correction circuit that would increase the power factor of such a circuit by decreasing the lag between current and voltage peaks. The most obvious solution to correcting a power factor is to place a capacitor across the primary winding of the transformer. However, the efficiency of low voltage capacitors (110 volts) is poor and in situations where capacitors are designed for operating in a high ambient temperature the capacitor would be physically large and, therefore, unacceptable in size and weight to the jet engine manufacturer.
Therefore, the specific problem presented to the inventor was to provide a 110 volt input capacitor discharge ignition system having nine joules of energy stored in a capacitor each time it was periodically discharged while limiting the input current to less than one AMP. Thus, since the capacitor was to be charged and discharged two times per second and since size and weight were to be minimized, this posed a difficult problem.